Experiments are proposed to establish a more rational basis for drug discovery in migraine and related headaches. This area of investigation has been supported by the NIH for the past 11 years. Migraine, the 2nd leading cause of work loss, afflicts up to 15% of people with a predominance of females (3:1). Antimigraine drugs (e.g., sumatriptan and valproate) reduce neurogenic inflammation (NI) within rodent dura mater and decrease c-fos immunoreactivity within trigeminal nucleus caudalis (TNC) following noxious meningeal stimulation. Sumatriptan and related compounds might decrease headache by acting on 5-HT1D receptors located either on trigeminal nerve fibers or on vascular smooth muscle (or both). Experiments in Aim 1 are intended to define the presence/absence and importance of 5-HT1B/D receptors subtypes on trigeminal fibers to NI and c- fos expression. In the absence of drugs which discriminate between 5- HT1Dalpha\beta, we propose to use knockout mice lacking 5-HT1B or 5- HT1Dalpha receptors to address the relevance of these sites in NI, c-fos expression, and pial vasomotor responses using a cranial window. We also propose to use antisense strategies to test whether 5-HT1Dalpha mRNA blockade inhibits the effects of agonists on NI or c-fos expression after noxious meningeal stimulation. We propose to extend the relevance of rodent data to humans by comparing receptor binding and gene expression within rodent and human trigeminal ganglions and related postmortem tissues using receptor autoradiography, in situ hybridization, and RT-PCR techniques. Specific Aim II will examine the possible importance of a recently proposed therapeutic target in migraine therapy (GABAA) and extend preliminary data showing that valproate (which blocks GABA degradation) blocks NI within the meninges by bicuculline-sensitive mechanisms. Studies will determine whether the receptor is outside the blood brain barrier (BBB) (like 5- HT1D), and by so doing, suggest alternative therapeutic approaches using BBB impermeant GABAergic drugs. We will extend preliminary data showing that GABAA agonists and modulators (i.e., neurosteroids, and benzodiazepines) are dependent upon the integrity of parasympathetic nerves innervating the meninges. Molecular strategies including in situ hybridization and RT-PCR will be used to confirm the subtype and establish the location of GABA receptors within human and rodent meninges.